That's a bad idea. Windows automatically detects the number of cores and can use 256 at once. If Windows doesn't use all 8 cores under load situations, that's a BIOS issue. Intel Core iX and Xeon 5500 CPUs disable cores to save power and turn them back on
when needed. This however requires BIOS and operating system support. Using the BIOS, power capping can be forced to do all kinds of funny things, though. Usually you'll find relevant options there.

You shouldn't change the kernel options from the defaults, that may have funny results. If for whatever reason those options were set, there should have been a reason for it, even if unchacked is the default.

That's a bad idea. Windows automatically detects the number of cores and can use 256 at once. If Windows doesn't use all 8 cores under load situations, that's a BIOS issue. Intel Core iX and Xeon 5500 CPUs disable cores to save power and turn them back on
when needed. This however requires BIOS and operating system support. Using the BIOS, power capping can be forced to do all kinds of funny things, though. Usually you'll find relevant options there.

You shouldn't change the kernel options from the defaults, that may have funny results. If for whatever reason those options were set, there should have been a reason for it, even if unchacked is the default.

Thanks for the tip Dovella, but that suggestion is for boot time only. I was wondering about normal execution after boot. And they were already unchecked from the beginning, I did not change that.

I would like to reiterate that I find all my cores work to full capacity when the CPU gets busy, so Windows is doing things right already. I was merely curious why Windows chose to keep some specific cores idle. For example, in Ubuntu under very light load,
I find that 2 cores are being used at any given time, and it cycles in a round-robin manner.

Thanks for the tip Dovella, but that suggestion is for boot time only. I was wondering about normal execution after boot. And they were already unchecked from the beginning, I did not change that.

I would like to reiterate that I find all my cores work to full capacity when the CPU gets busy, so Windows is doing things right already. I was merely curious why Windows chose to keep some specific cores idle. For example, in Ubuntu under very light load,
I find that 2 cores are being used at any given time, and it cycles in a round-robin manner.

Well... as mentioned before Windows might do core parking. This means that the cores are shut down and power is saved. In my opinion that's an ideal behaviour because why would you keep all cores powered up if you only need a subset of them because of not
much really going on?

Thanks for the tip Dovella, but that suggestion is for boot time only. I was wondering about normal execution after boot. And they were already unchecked from the beginning, I did not change that.

I would like to reiterate that I find all my cores work to full capacity when the CPU gets busy, so Windows is doing things right already. I was merely curious why Windows chose to keep some specific cores idle. For example, in Ubuntu under very light load,
I find that 2 cores are being used at any given time, and it cycles in a round-robin manner.

no, sorry, perhaps I expressed myself badly.This is a bug in Windows 7

FWIW. 64-bit is nothing but a pain to me. No silverlight on 64 IE for one. Had IE back button issues until just the other day a SP seemed to fix it . Drivers lag behind and not as tested as the more popular 32. Other strange print and pdf issues can pop up with apps like QB and more. I would just change back to win7 32 if it was not so much work at this point. I want to love it, but just do not see where it helps me in any way.

If you want to stress your system, throw video encoding at it. It is one of the few things that will pretty much always stress a system. I have a Core2Quad at home and a i7 at work, it is one of the few things that spikes my processor now a days.

@staceyw: really? I've been on x64 Win7 builds since it was in beta, I run x64 builds for most apps and stuff works great. I will say older hardware tends to not have x64 drivers however.

Only real driver issue I had was a driver from a USB wifi adapter that was pretty old. While I'm not thrilled when it effects me, I do understand when hardware makers do stuff like that. There is a cost for making and supporting.